[sdiy] Futurlec has LM394's for cheap

[René Schmitz]

Hi Grant and all,

Grant Richter wrote:
> Gain matching is not that important in exponential conversion.
> One side is just used to develop a temperature dependent Vbe offset,  to 
> cancel the other side.
> 
> Vbe matching is good, but can be trimmed at input op-amp.
> 
> Performance only needs to be good enough for music.
> Beyond that, it is a waste of money.

Amen.

> I have built VCO expo converters using every kind of matched pair.
> Properly adjusted, they will all track each other with a keyboard.

Exactly.

Those super matched pairs really make sense in applications where they 
can play out their low offset drift and good noise performance. (For me 
that means VCAs...)

Rbe is not the ultimate figure of merit, since you can compensate for 
it, and the compensation is almost perfect, and you need to do this 
anyway whether the Rbe is 1.2 or 0.3 ohms.

Cheers,
  René


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uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159